1. Field of the Invention
The present invention relates to a device activated by an optical signal. More particularly, it relates to an improvement of the assembled structure with the device.
2. Description of the Prior Art
FIG. 1 shows the conventional light-activated semiconductor device.
In FIG. 1, the reference numeral (1) designates the semiconductor substrate of a light-triggered thyristor having a light receiving part at the central portion; (2) designates a supporting plate made of molybdenum which is bonded on the semiconductor substrate (1) with a hard solder and is used as one electrode; (3) designates the other electrode brought into ohmic contact with the semiconductor substrate (1); (4) designates the other supporting plate made of molybdenum which is brazed to the electrode (3); (7) designates a copper base as one main electrode through which heat is transferred to a heat sink; (5) designates a brazing material for hermetically bonding the supporting plate (4) to the copper base (7); (9) designates an outer electrode as the other main electrode; (8) designates an insulating plate made of ceramic or glass etc. which insulates the outer electrode (9) from the copper base (7); (13) designates a metallic tube hermetically bonded to the insulating plate (8) and the copper base (7); thus an outer casing is formed by the copper base (7), the insulating plate (8) and the outer electrode (9); (6) designates a flexible inner lead wire brazed to the supporting plate at one end and crimped to the outer electrode at the other end; (10) designates a light cable inserted into the central through-hole of the copper base (7) and extending to the light receiving part of the semiconductor substrate (1); (11) designates a core consisting of a group of glass fibers at the center of the light cable (10); (14) designates a cover of the light cable (10) and (12) designates silicone rubber for protecting the exposed part of the PN junction of the semiconductor substrate (1).
In the conventional light-activated semiconductor device, the core (11) is formed by a single glass fiber having a diameter of 100 .mu.m or less, or by a plurality of glass fibers shown in FIG. 1 and the cover (14) of the light cable (10) should be slidable relative to the core (11) in order to provide flexibility of the light cable (10). In this structure, it is impossible to attain a hermetic seal. Accordingly, the brazing material (5) is applied so as to completely seal around the casing so that the deterioration of voltage blocking characteristics caused by the exposing of the PN junction surface of the semiconductor substrate (1) can be prevented.
The disadvantages of the conventional light-activated semiconductor device are as follows; a main surface of a semi-conductor element comprising the semiconductor substrate (1), the supporting plate (2), the electrode (3) and the supporting plate (4) must be brazed on a part of the casing (e.g. the copper base (7) in FIG. 1) and accordingly, the occurrence of thermal fatigue of the brazing material (5) can not be prevented even though the supporting plate (4) made of molybdenum is provided; and the curvature of the light cable (10) can not be small when the light cable is employed in a device having a flat-shaped surface-cooling type casing (the small curvature results in a great increase of the light cable loss) and accordingly, it is difficult to employ the light cable in such a device.